In blast furnaces, steel mills, iron and steel foundries, and other similar facilities a variety of different ladles and other vessels and conduits are required for transporting, processing, and storing molten or near-molten metal at temperatures in excess of 1600.degree. F., the metal temperature sometimes exceeding 3000.degree. F. In many instances, the molten metal is accompanied by at least limited quantities of slag. In the past, and even up to the present time, many of these transportation and storage vessels and conduits have been left open to the atmosphere, often producing substantial undesirable emissions and surface chemical reactions. Open vessels and conduits also result in high heat losses having an adverse economic impact on operation of the facilities in which they are employed. Another problem encountered in facilities of this kind is the solidification of metal remaining in vessels or conduits after they have been drained, with a consequent loss of capacity. Yet another problem for such vessels and conduits results from thermal shock to the refractory lining if the vessel or conduit is drained and remains empty and open to the atmosphere for a substantial period of time prior to re-use.
In some blast furnaces, steel mills, foundries, and like facilities, the foregoing problems pertaining to undesirable emissions, heat losses, thermal shock, and metal solidification are reduced by providing covers for the vessels and conduits. For the most part, these covers have been of rigid construction and have included refractory linings facing the interiors of the vessels or conduits. These covers have generally been quite heavy, so that they cannot be removed or replaced manually. As a consequence, a crane or hoist is required to remove such a cover for filling or emptying a ladle, tundish or other vessel or for repair and maintenance of a trough, runner, or similar conduit. Another problem with rigid covers is the necessity of maintaining a refractory insulator lining in place on the lower surface of the cover; any fastening means for the refractory lining tends to deteriorate with continued use, which may lead to all or part of the refractory lining dropping into the vessel or conduit with consequent contamination of the metal.
Attempts have been made to meet these difficulties through the use of covers of light weight, flexible, fibrous ceramic insulator materials sometimes referred to as ceramic "blankets". Thus, for a vessel used for the transportation of molten iron or steel, it has been known to place a ceramic blanket over the inlet opening of the vessel and to maintain that blanket in place while the vessel is used to transport the molten metal. A ceramic blanket of this kind, however, is relatively fragile, at least in comparison with other devices used in a blast furnace, steel mill, foundry, or similar environment. Thus, the ceramic blanket is subject to devitrification when directly exposed to the interior of a vessel or conduit containing molten iron or steel for an extended period of time. The ceramic blanket is also likely to be severely damaged if contacted by any of the molten metal.
The surface of a ceramic blanket is also quite subject to abrasion damage, and dimensional stability of the blanket material leaves much to be desired. In some instances, open mesh metal facings have been utilized on ceramic blankets of this kind, the mesh frequently being a type that resembles conventional chicken wire. A facing of this kind provides some improvement in the life of a ceramic blanket cover for a vessel or conduit used in the transportation or storage of molten metal, but even with such a facing, the ceramic blanket has a relatively short useful life, usually only a few hours. In this regard, the labor cost entailed in frequent replacement of the ceramic blanket can be substantial.
Thus, there is a major need for a light weight insulator cover capable of extended, repetitive use on a vessel or conduit employed in transporting, processing, or storing molten or near-molten metal as in a blast furnace, steel mill, foundry, or other like facility. Such a cover or cover material should be light enough in weight to permit effective positioning and removal of the cover by one man or at most by two men. The cover should not have the fragility of a conventional ceramic insulator blanket; that is, it should have good dimensional stability, should remain relatively unaffected by exposure of extended duration (e.g. several days to several weeks) to molten or near-molten metal, and should exhibit high resistance to deterioration from abrasion and other physical shocks occurring in the course of removal and replacement of the cover. At present, covers and cover materials having these characteristics are not available.